There have been numerous different types of mechanisms employed in piano key action. As is well known in the trade, the term "key action" and mechanism thereof refers to the mechanical chain of levers and combinations of levers which result in ultimately the piano key-hammer(s) striking the piano string(s) as the pianist plays on the keys. Additionally, however, it refers to the extent to which there is ease or alternately difficulty, sensitivity or alternately lack of sensitivity, to the force utilized in striking the piano key(s). It is noteworthy that the employment and use of a piano "soft pedal" of a piano reflects the recognition of lack of sensitivity of key action. Mere key action has in the past made it impossible to effectively or adequately play (strike) a key with varying degrees of force or touch as to obtain desired expression such as pianissimo, in playing a musical composition on the piano keys. The soft pedal when utilized, shifts the entire piano carriage and/or keys relative to position(s) of the piano string(s) such that the hammer(s) strike fewer strings for the same note--with a resulting softness (less loud) because fewer strings have been struck. The soft pedal approach amounts to all or nothing logic.
In conventional grand piano arrangement, with regard to a pivoted fly lever pivotably mounted on a distal end of a pivoted wippen lever, a fly lever's distal end freely passes through a space defined between forks, spaced-apart flanges, in a distal end of a thrust balance lever, with the fly lever's distal end being directly in contact with and supporting solely a lower face of an abutment mounted on a lower face of an intermediate portion of a pivoted hammer shaft. That arrangement is such that pivotal sideward movement of a fly lever's distal end from a supporting position and state beneath the pivoted shaft's abutment, results in the hammer-shaft lever abutment abruptly jerking downwardly while substantially concurrently a fly lever's distal end is impelling upwardly the hammer-shaft lever; when a hammer shaft lever abutment snaps downwardly as a result of the final full pressing downwardly on a piano key's proximal end, taken with movement of a fly lever's distal end from its supporting position, thereafter (until a full total repeat/return movement of all levers after release of downward pressure on the piano key's proximal end) the hammer-shaft's abutment comes to rest on an upper surface of spaced-apart flanges of the thrust balance lever. In that type of arrangement of elements, prior to the fly lever's distal end totally slipping from its supporting position, further upward movement of the distal end of the thrust balance lever has been thwarted by stop-structure. Accordingly, as a result of the thrust balance lever having been pivotally mounted at an intermediate portion thereof onto the wippen lever, the blocked further upward movement of the thrust balance lever's distal end causes the proximal end of the thrust balance lever to tend to move upwardly against downwardly-biasing stress of a tension spring, with a resulting increasing build-up of stress and tension. Accordingly, when the distal end of the wippen lever's distal end moves upwardly, driving upwardly the fly lever pivotally mounted thereon, the distal end of the fly lever by the above-noted increasing force and tension, increased pressure of the upper-end face of the fly lever is further caused to increase tension and stress as a result of the ever-increasing pressure of the fly lever's distal end against the lower face of the hammer-shaft's abutment. Eventually, as a result of continually increasing pressure and upward speed of movement of the fly lever's upper-end face, the pivoted hammer shaft is thereby caused to pivotably flip-upwardly as concurrently the excessive pressure, taken together with lever action of a lower proximal end of the fly lever against an abutment mounted on the support structure, causes the fly lever's upper-end face to sidewardly pop-out from beneath the hammer-shaft abutment' s lower face. The above-described mechanism and action results in a high degree of friction, and action involving forceably popping-out or snapping-out from its supporting position. As a result of this type of action, it is virtually impossible to effectively vary the extent of jerking-action with any appreciable degree of sensitivity. This is to say, there is always the area of lack of control as a result of the inherent mechanism of that type of key action mechanism. Except for the extremes of lightly touching a piano key's proximal end during playing the piano, as opposed to pounding (with great force striking) the key, together with the use of a soft pedal to soften the intensity of key string sound when the string(s) are struck, expressions of intermediate degrees of loudness or softness have been substantially impossible. A typical patent illustrating a mechanism of this general type is the present inventor's U.S. Pat. No. 2,540,871 dated Feb. 6, 1951. The typical and more expensive and elegant grand pianos such as the Steinway pianos, embody the mechanism discussed in this paragraph.
In another type of key action mechanism as is typically shown and represented in the present inventor's Finholm U.S. Pat. No. 2,156,913 dated May 2, 1939, the distal end of the fly lever supports solely the lower face of the distal end of the thrust balance lever, and solely the thrust balance lever distal end's upper face supports the lower face of the hammer shaft abutment. The remaining mechanism of this 1939 patent is otherwise considerably different from the mechanism and structure of the 1951 patent and from that of the present invention.
In the Steinway and other similar grand pianos, there are two separate leaf springs employed, mounted on the wippen lever. One leaf spring--as above-noted, biases upwardly the thrust balance lever distal end against the above-noted "stop", relative to the wippen lever on which the thrust balance lever's distal end is mounted, as it moved upwardly. The thrust balancing lever's intermediate portion is pivotally mounted on the intermediate portion of the pivotally-mounted wippen lever. The other leaf spring biases the fly lever's distal end toward the position at which the fly lever distal end supports the hammer lever abutment. There are competing and counter-productive forces in operation in such prior art key action-arrangement. As a result of the return-action biasing on the fly lever, greater upward force of the fly lever's distal end against the hammer-shaft's abutment is required prior to the fly-lever's distal end popping-out from its support position. Once the "stop38 comes into operation, this also amplifies the great magnitude or intensity of the jerking-action when the fly lever's distal end snaps from beneath the hammer-shaft abutment. Also, in order to achieve sufficient thrust against the hammer-shaft's abutment to effectively propel the hammer with sufficient force against the piano string(s), it is required the fly lever have a relatively long dimension, there being a minimal length at which it would effectively operate. Likewise, in the mechanism above-described for the Steinway type arrangements, the "stop" that initiates the stress eventually leading to the fly lever's distal end popping-out from beneath the hammer-shaft's abutment, results in greater stress as length of the fly lever employed is increased. Such great stress inherently is present during the key action as a result in part, of the essential long fly lever, taken together with the "stop" that prevents further upward movement of the thrust balance lever's distal end. As above-noted, the ultimate result in that type of arrangement is a lack or loss of control of sensitivity to the "touch"--with regard to softness or loudness, when the key(s) are struck. The high tension necessitated prior to the fly lever's distal end snapping-out from its supporting position of and from beneath the pivoted hammer-shaft abutment, tremendously increases the amount of friction between the fly lever distal end and the lower face of the hammer-shaft abutment. Accordingly, this friction point has always been a most objectionable feature in a piano artist's attempting to play pianissimo, for one either pressed the key too far or not far enough, being hindered by friction during release of the fly lever's (jack's) distal end and pressurized resistance of the repetition drop screw--i.e. the above-noted stop. Also, because of the undesired large amount of friction and the wear and tear associated therewith, the life of a particular adjusted mechanism is extremely short, the mechanism being hypersensitive to such wear and tear; the result is frequent and recurring breakdowns--right up to and during concerts on the piano, apart from the inherent lack of control and lack of sensitivity always experienced by the pianist.